Answer:
Option 2, The color of the feeder
Step-by-step explanation:
In this experiment the researcher want to study whether the hummingbirds are attracted to red feeders. In this scenario all the features of red feeders which are able to grasp the attention of humming bird can be considered as independent variable. As an independent variable is the one which does not depend on any other factor but is responsible for the controlling the output of the research , the option 2 “the color of the feeder” seems to be the correct choice of answer as the rate/extent to which the humming bird is attracted towards the red feeder depend on the bright color of the feeder